For many years, hermetic sealing of enclosed bearing housings has been the goal for the efficient operation of rotating equipment. Minimum maintenance of rotating equipment is of increasing importance to operators because of the necessity to improve efficiency. Minimum maintenance is difficult to obtain because of the extreme equipment duty cycles, the lessening of service factors in design and the lack of spare rotating equipment in many processing plants.
Various forms of shaft sealing devices have been utilized to try to protect the integrity of the bearing environment including rubber lip seals, clearance labyrinth seals and attraction magnetic seals. Rubber lip seals were first utilized to connect the bearing frame to the rotatable shaft in an attempt to isolate the bearings from exterior contamination. Such lip seals are subject to premature wear and are short-lived. Lip seals also have been known to permit excessive amounts of moisture and other contaminants to become present in the oil reservoir of the bearing frame of the operating equipment.
Labyrinth-type seals involving closely related stator and rotor rings which do not contact each other, but define labyrinth passages between them, have been devised and utilized and are illustrated in U.S. Pat. No. 4,706,968. This type of seal also allowed a certain amount of axial separation of the fixed ring and the rotating ring to prevent contact and wear between sealing members and thus enhance the sealing characteristics. Labyrinth seals also allowed free transfer of humid vapors in and out of the bearing frame.
Mechanical shaft seals of the non-magnetic type have also been utilized as shaft sealing devices. This type of seal employs the use of metallic springs of the coil design or welded metal bellows design to effect the closure of the sealing faces. The metal springs of either design are subject to corrosion, fatigue, product fouling and stress over time and are linear in response to opening and closing of the sealing faces. This linear response does not adequately maintain the sealing surfaces as wear or corrosion continues to occur.
Attraction magnetic sealing systems have also been utilized as sealing devices. In this case, the attraction magnetic seal systems rely upon magnetic attraction to maintain face closure integrity and these seals are exemplified and described in U.S. Pat. No. 4,795,168 and the references cited therein. These attraction magnetic sealing systems are subject to exterior system forces that tend to separate the relatively rotating sealing faces. This works against the principle of magnetic attraction. When the sealing faces are separated, the forces of the magnetic field are weaker and the tendency for failure in operation by further separation and further weakening is pronounced. If there is wear between the sealing surfaces, then the magnetic forces are pulled closer together and the wear rate increases exponentially. This also increases the failure rate due to the increased torque required as the magnetic field increases. Magnetic or magnetized components of the attraction-type magnetic seals are typically attempted to be insulated from ferrous bearing housings to isolate the magnetic field from the bearings and/or housing. However, there are no true insulators against magnetism and the attempts to insulate the magnetic fields have greatly increased the structural complexity and cost without any benefits.
The present invention concerns the use of magnetic principles where the magnetic orientation is designed to seal by repelling one of the sealing components. The sealing interface is loaded with a controlled amount of axial force. The value of this axial force is determined by the axial proximity of the opposing magnets as well as the magnetic force of the opposing magnets. In addition, the magnetic flux lines are directed away from the sealing interface and do not have a tendency to magnetize a ferrous bearing housing. In this invention, a stationary sealer ring, i.e., the stator, functions as an insert in the bore of the bearing frame. The stator can be made from any material that is suitable for optimum sealing performance and yet does not have to be attractive to a magnetic force or be magnetized or be a magnet as is the case with the sealing faces of attraction magnetic sealing devices.